This section is from the book "A Practical Treatise On The Joints Made And Used By Builders", by Wyvill J. Christy. Also available from Amazon: Practical treatise on the joints made and used by builders.
This is the same as in bricklayers' work. There are one or two exceptions, however, inasmuch as external architraves and other stone dressings introduce a long description of perpendicular joint which should be concealed as much as possible by the overlap of mouldings and rebates, as noticed under Back Rebate Joint. The drums or shafts of columns should have no vertical joints except from economical motives. In ashlar the perpendicular joints on the face should be exactly over each other, and in coursed rubble the lap of one stone over another should never be less than 3 in. The apex or saddle stones of pediments, gables, and raking cornices should have no perpendicular joint, whilst some allege that a central one is characteristic of the Gothic arch.
Pinned Joint is made by pinning in, which consists in letting into a hole either expressly cut or left, or otherwise provided, the end of a step, beam, or girder, or of almost any piece of iron, slate, stone, etc, and solidly and firmly securing it therein by tightly filling the joint all round with cement, and working and jamming in pieces of tile, old iron, slate, etc, so as to produce thorough compactness and make the joint a source of strength, if that were possible. Stone landings and hanging steps are thus pinned in to a depth ranging from 4½ in. to 14 in., according to the thickness of the wall.
Plugged Joint occurs when a side joint is secured against working loose by means of a plug, often consisting of lead, which is run through a vertical groove into a double dovetailed plug hole that is partly cut out of each stone, as in Fig. 18. In such positions, plugs ought to reach nearly half way down the stones. There are different shapes given to the hole, the object in all being to enlarge the ends of the plug to stop it from drawing. It also is formed when a bed-plug of hard wood, stone, slate, or metal is inserted in opposite mortise holes, or otherwise, in a raking, level, or radiating bed joint in arches, tracery, mullions, copings, etc, to prevent sliding.
This kind of plug should not be less than 1 in. square, but need not be larger than about 3 in. square and 4 in. long when the blocks are of considerable size. In masonry it is no uncommon thing to attach an identical meaning to the terms plug and dowel.
Pointed Joint is effected by finishing off a joint with the point of the trowel in any regular and neat manner. It may be either the original bed joint or else that formed by subsequent raking out and stopping. The term includes making good an open and defective joint, pressing and squeezing in the mortar so as to fill up all cavities, and in some cases even comprehends bedding as well. Rubble walling is often pointed with coal ash or blue mortar. Whenever joints are raked out, they require well brushing and wetting before pointing, and where face stones and cement bond courses are bedded in Portland or other hard-setting cement, they should invariably be raked out clean an inch or so back as soon as the block is laid, or before the cement has had time to set, otherwise there will be a risk of damaging the arrises in pointing, and of not making the face joints preserve an equal thickness.